System and method for ultrasound distance detection

Abstract

A system for using ultrasound to detect distance on mobile platform and methods for making and using same. The system includes an ultrasound transceiver that can transmit and/or receive ultrasound waves and determine distance from an object of interest using a time-of-flight of the ultrasound wave. The system is adapted to reduce noise by using a dynamic model of the mobile platform to set constraints on the possible location of a received ultrasound echo. A linear, constant-speed dynamic model can be used to set constraints. The system can further reduce noise by packetizing a received ultrasound waveform and filtering out noise according to height and width of the packets. The system likewise can remove dead zones in the ultrasound transceiver by subtracting an aftershock waveform from the received waveform. The systems and methods are suitable for ultrasound distance detection on any type of mobile platform, including unmanned aerial vehicles.

What is claimed is: 
     
       1. A method of ultrasound distance detection for a mobile platform, the method comprising:
 emitting an ultrasound wave from the mobile platform; 
 estimating, based on a dynamic model and using a state of the mobile platform at a time when the ultrasound wave is emitted, a state of the mobile platform at a time when an ultrasound echo of the ultrasound wave, which is reflected by an object, is expected to be received by the mobile platform, the state of the mobile platform including a position of the mobile platform and a change of the position of the mobile platform over time, and the dynamic model including a relationship between the state of the mobile platform, a change of the state of the mobile platform over time, and an assumed noise; 
 predicting a location of the mobile platform at the time when the ultrasound echo of the ultrasound wave is expected to be received by the mobile platform based on an average value and a variance of the state of the mobile platform at the time when the ultrasound echo of the ultrasound wave is expected to be received by the mobile platform; 
 determining a set of timing constraints on a timing of the ultrasound echo being received by the mobile platform using the predicted location of the mobile platform, including determining a width and a position of the timing constraints according to the average value and the variance, respectively, of the state of the mobile platform at the time when the ultrasound echo of the ultrasound wave is expected to be received by the mobile platform; 
 identifying the ultrasound echo from a received sonic waveform within the timing constraints, including distinguishing the ultrasound echo from noise on the received sonic waveform by:
 dividing the sonic waveform into packets; and 
 filtering the packets using a threshold packet bandwidth or amplitude to identify one of the packets that corresponds to the ultrasound echo, the threshold packet bandwidth being multiple of an average width of previously known echoes, and the threshold packet amplitude being a fraction of an average amplitude of the previously known echoes; and 
 
 determining a distance between the mobile platform and the object based upon the ultrasound echo. 
 
     
     
       2. The method of  claim 1 , further comprising, prior to said identifying:
 determining an aftershock waveform resulting from residual vibrations in an ultrasound transmitter of the mobile platform emitting the ultrasound wave; and 
 subtracting the aftershock waveform from the received sonic waveform. 
 
     
     
       3. The method of  claim 2 , wherein said determining the aftershock waveform comprises receiving the sonic waveform under reduced echo and/or reduced noise conditions and determining the aftershock waveform based on the received sonic waveform. 
     
     
       4. The method of  claim 2 , wherein said determining the aftershock waveform comprises determining a timing of the aftershock waveform relative to a corresponding ultrasound emission, and wherein said subtracting the aftershock waveform comprises subtracting the aftershock waveform according to the timing. 
     
     
       5. The method of  claim 1 , wherein the dynamic model is a linear dynamic model. 
     
     
       6. The method of  claim 1 , wherein the dynamic model is a non-linear dynamic model. 
     
     
       7. The method of  claim 1 , wherein the dynamic model is a fixed-speed dynamic model, a planar dynamic model, or a non-planar dynamic model. 
     
     
       8. An apparatus for ultrasound distance detection comprising:
 an ultrasound transmitter for emitting an ultrasound wave; 
 an ultrasound receiver for receiving an ultrasound echo of the ultrasound wave, which is reflected by an object; and 
 a processor configured to:
 estimate, based on a dynamic model and using a state of a mobile platform at a time when the ultrasound wave is emitted, a state of the mobile platform at a time when the ultrasound echo is expected to be received by the mobile platform, the state of the mobile platform including a position of the mobile platform and a change of the position of the mobile platform over time, and the dynamic model including a relationship between the state of the mobile platform, a change of the state of the mobile platform over time, and an assumed noise; 
 predict a location of the mobile platform at the time when the ultrasound echo of the ultrasound wave is expected to be received by the mobile platform based on an average value and a variance of the state of the mobile platform at the time when the ultrasound echo of the ultrasound wave is expected to be received by the mobile platform; 
 determine a set of timing constraints on a timing of the ultrasound echo being received by the mobile platform using the predicted location of the mobile platform, including determining a width and a position of the timing constraints according to the average value and the variance, respectively, of the state of the mobile platform at the time when the ultrasound echo of the ultrasound wave is expected to be received by the mobile platform; 
 identify the ultrasound echo from a received sonic waveform within the timing constraints, including distinguishing the ultrasound echo from noise on the received sonic waveform by:
 dividing the sonic waveform into packets; and 
 filtering the packets using a threshold packet bandwidth or amplitude to identify one of the packets that corresponds to the ultrasound echo, the threshold packet bandwidth being multiple of an average width of previously known echoes, and the threshold packet amplitude being a fraction of an average amplitude of the previously known echoes; and 
 
 determine a distance between the mobile platform and the object according to the ultrasound echo. 
 
 
     
     
       9. The apparatus of  claim 8 , wherein the processor is further configured to, prior to identifying the ultrasound echo:
 determine an aftershock waveform resulting from residual vibrations in an ultrasound transmitter of the mobile platform emitting the ultrasound wave; and 
 subtract the aftershock waveform from the received sonic waveform. 
 
     
     
       10. The apparatus of  claim 9 , wherein the aftershock waveform is determined by receiving the sonic waveform under reduced echo and/or reduced noise conditions. 
     
     
       11. The apparatus of  claim 9 , wherein the processor is configured to determine a timing of the aftershock waveform relative to a corresponding ultrasound emission and subtract the aftershock waveform from the received sonic waveform according to the timing. 
     
     
       12. A mobile platform comprising:
 an ultrasound transmitter for emitting an ultrasound wave; 
 an ultrasound receiver for receiving an ultrasound echo of the ultrasound wave, which is reflected by an object; and 
 a processor configured to:
 estimate, based on a dynamic model and using a state of the mobile platform at a time when the ultrasound wave is emitted, a state of the mobile platform at a time when the ultrasound echo is expected to be received by the mobile platform, the state of the mobile platform including a position of the mobile platform and a change of the position of the mobile platform over time, and the dynamic model including a relationship between the state of the mobile platform, a change of the state of the mobile platform over time, and an assumed noise; 
 predict a location of the mobile platform at the time when the ultrasound echo of the ultrasound wave is expected to be received by the mobile platform based on an average value and a variance of the state of the mobile platform at the time when the ultrasound echo of the ultrasound wave is expected to be received by the mobile platform; 
 determine a set of timing constraints on a timing of the ultrasound echo being received by the mobile platform using the predicted location of the mobile platform, including determining a width and a position of the timing constraints according to the average value and the variance, respectively, of the state of the mobile platform at the time when the ultrasound echo of the ultrasound wave is expected to be received by the mobile platform; 
 identify the ultrasound echo from a received sonic waveform within the timing constraints, including distinguishing the ultrasound echo from noise on the received sonic waveform by:
 dividing the sonic waveform into packets; and 
 filtering the packets using a threshold packet bandwidth or amplitude to identify one of the packets that corresponds to the ultrasound echo, the threshold packet bandwidth being multiple of an average width of previously known echoes, and the threshold packet amplitude being a fraction of an average amplitude of the previously known echoes; and 
 
 determine a distance between the mobile platform and the object according to the ultrasound echo. 
 
 
     
     
       13. The mobile platform  claim 12 , wherein the processor is further configured to, prior to identifying the ultrasound echo:
 determine an aftershock waveform resulting from residual vibrations in an ultrasound transmitter of the mobile platform emitting the ultrasound wave; and 
 subtract the aftershock waveform from the received sonic waveform. 
 
     
     
       14. The mobile platform of  claim 13 , wherein the aftershock waveform is determined by receiving the sonic waveform under reduced echo and/or reduced noise conditions. 
     
     
       15. The mobile platform of  claim 13 , wherein the processor is configured to determine a timing of the aftershock waveform relative to a corresponding ultrasound emission and subtract the aftershock waveform from the received sonic waveform according to the timing. 
     
     
       16. A non-transitory computer-readable medium with instructions stored thereon that, when executed by a processor, perform a method comprising:
 instructing an ultrasound transmitter to emit an ultrasound wave; 
 estimating, based on a dynamic model and using a state of a mobile platform at a time when the ultrasound wave is emitted, a state of the mobile platform at a time when an ultrasound echo of the ultrasound wave, which is reflected by an object, is expected to be received by the mobile platform, the state of the mobile platform including a position of the mobile platform and a change of the position of the mobile platform over time, and the dynamic model including a relationship between the state of the mobile platform, a change of the state of the mobile platform over time, and an assumed noise; 
 predicting a location of the mobile platform at the time when the ultrasound echo of the ultrasound wave is expected to be received by the mobile platform based on an average value and a variance of the state of the mobile platform at the time when the ultrasound echo of the ultrasound wave is expected to be received by the mobile platform; 
 determining a set of timing constraints on a timing of the ultrasound echo being received by the mobile platform using the predicted location of the mobile platform, including determining a width and a position of the timing constraints according to the average value and the variance, respectively, of the state of the mobile platform at the time when the ultrasound echo of the ultrasound wave is expected to be received by the mobile platform; 
 identifying the ultrasound echo from a received sonic waveform within the timing constraints, including distinguishing the ultrasound echo from noise on the received sonic waveform by:
 dividing the sonic waveform into packets; and 
 filtering the packets using a threshold packet bandwidth or amplitude to identify one of the packets that corresponds to the ultrasound echo, the threshold packet bandwidth being multiple of an average width of previously known echoes, and the threshold packet amplitude being a fraction of an average amplitude of the previously known echoes; and 
 
 determining a distance between the mobile platform and the object based upon the ultrasound echo. 
 
     
     
       17. The method of  claim 1 , wherein dividing the sonic waveform into the packets includes dividing the sonic waveform into time intervals having a duration based upon a frequency of the sonic waveform, the time intervals corresponding to the packets. 
     
     
       18. The method of  claim 1 , wherein dividing the sonic waveform into the packets includes using a peak selection technique to select the packets based on peaks in the sonic waveform. 
     
     
       19. The method of  claim 1 , wherein filtering the packets further includes discarding one of the packets that has an area less than a predetermined threshold value as noise.